Characterization and Localization of Dynamic Cell Wall Structure and Inorganic Species Variability in Harvested and Stored Corn Stover Fractions as Functions of Biological Degradation

Abstract

Traditional approaches for corn stover utilization create an inhomogeneous, whole plant mixture that does not achieve performance and cost targets for biofuel production. The improvement of conversion performance will require one to gain a fundamental understanding of the inherent cellular structure and ash content in the process. This study investigated cellular structure and inorganic species contents with scanning electron microscopy (SEM), advanced energy dispersive X-ray spectroscopy (EDS), and wet analytical chemistry methods. These techniques provided a complementary means to understand variability within the dynamic cell walls and the distributions of inorganic species at the anatomical and tissue scales for various corn stover fractions. Material properties were investigated for bales from in-field storage scenarios ranging from mild to severe biological degradation. Results show that stem, cob, and leaf tissues all maintained cell wall and surface structure integrity after mild biological degradation. However, severe degradation (with spontaneous heating) caused remarkable structural distortion and cell wall shrinkage for all tissue types. Inorganic species quantitation data shows that three fractions of severe degradation have slightly reduced total ash, 4.91% vs 3.92% for cobs, 7.28% vs 5.98% for stems, and 14.21% vs 13.07% for leaves. Silica contents also decreased (2.67% vs 1.83% for cobs, 3.60% vs 2.89% for stems, and 9.72% vs 8.48% for leaves), likely due to the loss of extrinsic inorganic species. SEM-EDS inorganic species mapping of stems demonstrated that severe biological degradation caused the translocation of the dominant silicon elements from pith to rind tissue as well as a reduction of potassium in the stem. These findings offer detailed knowledge of feedstock variability at the anatomical tissue level that can be used to inform the development of advanced processing strategies. Innovative storage and selective fractionation processes have the potential to manage low-quality fractions/tissues and remove unfavorable inorganic species for efficient conversion of corn stover as well as other lignocellulosic biomass.